Apparatus for prestressing concrete



June 3, 1969 P. LAUNAY 3,447,784

APPARATUS FOR PRESTRESSING CONCRETE Filed Jan. 5, 1966 Sheet of 6 June 3, 1969 P. LAUNAY 3,447,784

APPARATUS FOR PRESTRESSING CONCRETE Filed Jan. 3. 1966 Sheet 2 of s Fig. 5

June 3, 1969 P LAUNAY 3,447,784

APPARATUS FOR PRESTRESSING CONCRETE Sheet Q of 6 Filed Jan. 3. 1966 June 3, 1969 P; LAUNAY 4 APPARATUS FOR PRESTRESSING CONCRETE Filed Jan. 3. 1966 Sheet 4 of e Sheet '5 I Filed Jan. 3, 1966 June 3, 1969 P. LAUNAY 3,447,784

APPARATUS FOR PRESTRESSING CONCRETE Filed Jan. 5, 1966 Sheet 6 of a,

United States Patent ABSTRACT OF THE DISCLOSURE An apparatus for prestressing concrete including a tube extending through the concrete through which a tension rod or the like extends. On each end of the rod wedgeshaped gripping means are placed to hold said rod in a tensioned condition.

Claims 4 Claims The present invention has for an object apparatus for prestressing concrete by placing high resistance steel rods under tension in the concrete.

The present invention particularly applies where the rods are disposed within tubes in the concrete.

Another object of the present invention is to obtain correct centering of the rods in their tubes with anchorage devices for the rods in tensioned condition.

In accordance with the present invention, the apparatus comprises a rod, an anchoring device for the rod, a tube surrounding the rod, a centering device for the rod in the tube and an element associated with the anchoring device bearing on the concrete.

The present invention will now be described with reference to preferred embodiments thereof and to particular structures by way of example as shown in the accompanying drawings.

In the accompanying characters indicate like of a concrete form on of a bar under tension to stress the same;

FIGS. 2 and 3 show in perspective respectively a part of a collar and a part of a key, a collar and two keys comprising an anchoring device for the bar;

FIG. 4 shows another embodiment of the present indrawings, in which like reference parts, FIG. 1 is a partial section a plane passing through the axis vention in which the anchoring device is located within a receptacle in the concrete;

FIGS. 5 and 6 show variations analogous to the embodiments of FIGS. 1 and 4;

FIG. 7 is another embodiment of the present invention in which the anchoring device includes a nut mounted on threads on the bar;

FIG. 8 is an enlarged detail of a part of the threaded portion of the bar of FIG. 7;

FIG. 9 is another embodiment of the present invention analogous to that of FIG. 7; and

FIGS. 10 and 11 show variations of the device of the present concept in which the bars are replaced by cables.

FIGS. 1 to 3 show an embodiment of the invention in which the bar 1 is placed in associated structure before pouring of the concrete. Bar 1 is surrounded by tube 2 which is covered by the concrete. Tube 2 is extended at its extremities by an element 3 of tubular form of reduced diameters at 4 spaced about the periphery thereof in such a manner as to form protuberances which center bar 1 accurately within element 3. A hearing plate 5 surrounds the extremity of element 3. Plate 5 is secured to the structure surrounding bar 1 and centers bar 1 and tube 2. Plate 5 serves as a support for the apparatus for placing bar 1 under tension if this apparatus has no other base for this purpose and serves as a base for the apparatus maintaing the tension of bar 1. As a result, bar 1 3,447,784 Patented June 3, 1969 is not subject to parasitic bending when it is under tension.

Tube 3 can include an extension 6 through which a duct 7 is attached which opens to an etxerior of the concrete and may serve for the injection of liquid mortar into th space 8 between bar 1 and tube 2.

The anchoring device for bar 1 which bears on plate 5 includes a collar 9 shown partly broken away in perspective in FIG. 2 in such a way as to show the interior thereof. Two cylindrical grooves are formed within collar 9, as seen at 10, making an angle a with the axis 11 of collar 9 with the axes intersecting at a joint within the mass of concrete.

The two cylindrical grooves 10 are symmetrical with respect to the axial plane 12 of collar 9.

Each of grooves 10 of collar 9 receives a key 13 having an exterior surface corresponding to the interior surface of a groove 10.

The interior of each key 13 is formed as a circular half cylinder 14 to bear upon bar 1. As seen in FIG. 3, each surface 14 can be toothed or receive a special treatment giving it a greater hardness than that of bar 1.

The anchoring device, as described above, is used as follows. Bar 1 is first put in place with collar 9 and keys 13 mounted in grooves 10. The tensioning apparatus is then connected to bar 1 to place it under tension, the other end of bar 1 being held in place by any suitable means including another anchoring device as described above.

When the desired tension of bar 1 is attained, keys 13 are forced into collar 9 to engage bar 1 and the tensioning device is then released. Bar 1 is then maintained under tension by the anchoring device. This anchoring device is particularly efficient because the contact between the interior surface 10 of the grooves and the exterior surface 15 of the keys is never either spotty or linear but is a surface contact whatever the relative position between keys 13 and collar 9. An excellent distribution of pressures is therefore obtained. To provide a strong grip between bar 1 and keys 13, it is necessary to have a reduced coefiicient of friction between surfaces 10 and 15.

FIG. 4 shows an embodiment of the present invention as seen in FIGS. 1 and 3 in which tubular piece 3' is surrounded at an extremity by plate 5 and is extended by a metallic box 16 mounted within the concrete 17. Box 16 provides a cavity in the concrete to receive the anchoring device 9-13. 1 FIG. 5 shows another variation of the present concept in which bar 1 is put into position after the concrete is poured. In this situation, bar 1 is introduced into tube 2 and bearing plate 5 is put in place. A washer 18 is placed on plate 5 and is of a malleable material which is not susceptible to flow such as, for example, soft steel. Collar 9 is mounted on washer 18 and bar 1 is placed under tension. Bar 1 is then anchored under tension by keys 13.

Washer 18 compensates for any misalignment of the axes of plate 5 and of collar 9 and provides perfect centeringof bar 1 in tube 2.

FIG. 6 shows another variation of the present con ceptanalogous to that of FIG. 4 including a box 16 receiving the anchoring device. In this case, and differing from that of FIG. 4, plate 5 is placed at the bottom of box 16 and not at the extremity of the centering element 3.

FIG. 7 shows still another variation of the present concept in which the anchoring device as shown in FIG. 1 is not used and the device includes a thread and nut. A thread 19 is formed on an extremity of bar 1 and a nut 20 is mounted on this thread.

Centering of bar 1 in tube 2 is provided by tubular element 3 which is extended by hearing plate 5. Plate 5 is centered with respect to element 3 by a. shoulder 21 forming a base for element 3.

Thread 19 of bar "1 is obtained by flow of the metal of the bar with a special profile of the thread which is rounded to provide minimum reduction of the diameter of the bar at the bottom of the thread to provide a bar diameter closely approximating the normal diameter thereof. This construction is particularly suitable to the diameter closely approximating the normal diameter high mechanical characteristics of the steel of the bars.

The radius of the bottom of thread 21 is preferably approximately three times the value of the radius of the top of thread 22.

Further, the flats of the threads preferably form an angle of about 90 with each other.

The radius of the height of the thread is preferably equal to H being the height of the thread.

It has been proved that such a thread is particularly eflicient for the anchoring device. As in the embodiments discussed above, bar 1 is placed under tension by apparatus bearing on plate 5 after which nut 20 is turned into contact with plate 5 and the tensioning apparatus is released.

FIG. 9 shows a still further variation of the present invention including an anchoring device analogous to that shown in FIGS. 7 and 8 but applied to the situation in which bar 1 is put in position after casting of the concrete. In this situation, plate 5 is not mounted in the concrete as shown in FIG. 7 but rests on the surface of the concrete. This embodiment includes a washer 22 of malleable material not susceptible to flow, analogous to washer 18 shown in FIG. 5. Washer 22 assures coincidence of the axes of plate 5 and bar 1.

FIG. shows a concrete mass in which conduits 24 are formed covering a sheath 2. receiving twisted tensioning cables 25 and 26.

Plate 27 is mounted on the concrete and has orifices therein receiving cables 25 and 26. Collars 9 bear on plate 27 and keys 13 lock the cables in the collars.

FIG. 11 illustrates the situation in which the interior surfaces of the collars are formed directly in a bearing plate 28 and in which the axes of the keys 13 are parallel. Cables 25 and 26 are then spread by spacer 29 and held together by a ring 30.

The cables open into space 31 in the concrete.

It should now be apparent that the present invention in every way satisfies the several objectives discussed above. Changes in or modifications to the above described 4 illustrative embodiments of this invention may now be suggested without departing from the present inventive concept. Reference should therefore be had to the appended claims to determine the scope of this invention.

What I claim is:

1. Apparatus for prestressing concrete including a tube in the concrete, a tension element in said tube, an anchoring device at each end of said element, said anchoring device including a ring, the interior portion of said ring being formed as two circular portions of cylinders having axes intersecting the axis of said ring, the point of intersection of said taxes being within the concrete mass, and two keys having circular cylindrical exterior surfaces of the same diameter as the interior cylindrical surfaces of said ring mounted in said ring, said keys having circular cylindrical interior portions of the same diameter as and engaging said element.

2. Apparatus as described in claim '1 including a device for centering said element comprising protuberances in said tube centering said element.

3. Apparatus as described in claim 1, said element being a cable and said anchoring device including a plate resting upon the concrete and openings in said plate forming said rings receiving said keys anchoring a plurality of said cables.

4. Apparatus as described in claim 3, a plurality of said cables passing in parallel through said plate, said cables being separated by spaces in the concrete.

References Cited UNITED STATES PATENTS 2,270,240 1/ 1942 Freyssinet 52230 2,728,978 1/ 6 Birkennaier 22429 2,763,464 9/ 1964 Leonhardt 25429 2,988,794 6/1961 Gutt 254-29 X 3,137,971 6/1964 Rhodes 52-230 3,176,961 4/1965 Glass 25429 FOREIGN PATENTS 764,197 12/ 1956 Great Britain. 879,293 6/ 1953 Germany. 32,183 3/1957 Finland.

OTHER REFERENCES German Printed Application, George Schulz, 1, 154,609,

September 1963.

German Printed Application,

7 Rudolph Buhrer, 1,135,154, August 1962.

OTHELL M. SIMPSON, Primary Examiner. 

